The present invention is directed to detection of partial discharge events in power systems such as cables, motors and transformers, and more particularly to a method and apparatus for detecting partial discharge events on-line while the power system is in operation.
Partial discharge events in high-voltage power systems, such as high voltage power distribution cables, motors and transformers, are high-frequency discharges that take place in small portions of the system insulation. These discharges may have a duration on the order of ten to fifteen nanoseconds, and usually occur at a peak of the a.c. power cycle when electrical stress is highest within the insulation. Partial discharge events generate high frequency electromagnetic pulses that travel along the power systems.
High voltage equipment for use in electrical power systems is conventionally tested off-line for partial discharge activity that may indicate insulation defects and possible insulation failure. These conventional techniques typically involve coupling a capacitor in parallel with the equipment under test and measuring the discharge signals across an external impedance such as a resonant circuit. The resonant circuit expands the discharge current pulses in the time domain so that the pulses are easier to detect and measure. Both amplitude and phase of each partial discharge pulse may be recorded and analyzed relative to the test voltage. Apparatus of this character is not well suited for detection and analysis of partial discharge events in power systems while the systems are on-line.
It is therefore a general object of the present invention to provide a method and apparatus for detection and analysis of partial discharge events in an a.c. power system that are adapted for use on-line while the system is in operation, and that may be readily implemented for determining type and/or location of the partial discharges as they occur.